Packaged semiconductor device

ABSTRACT

A packaged semiconductor device includes a molded interconnect substrate having a signal layer including a first channel and a second channel on a dielectric layer with vias, and a bottom metal layer for providing a ground return path. The signal layer includes contact pads, traces of the first and second channel include narrowed trace regions, and the bottom metal layer includes a patterned layer including ground cut regions. DC blocking capacitors are in series within the traces of the first and second channel for providing AC coupling that have one plate over one of the ground cuts. An integrated circuit (IC) includes a first and a second differential input channel coupled to receive an output from the DC blocking capacitors, with a bump array thereon flip chip mounted to the contact pads to provide first and second differential output signals.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Provisional Application Ser. No.62/675,396 entitled “MIS Multi-Layer FC-QFN Package Structure for HighSpeed (56 Gbps+) Applications”, filed May 23, 2018, which is hereinincorporated by reference in its entirety.

FIELD

This Disclosure relates to high speed packaged semiconductor devices.

BACKGROUND

Some high speed signal/data devices such as re-timer circuits,repeaters, and clock synthesizers are high volume and medium-high pincount devices which are typically packaged in flip chip ball grid array(FC BGA) packages, which are relatively high cost packages. Acost-effective alternative is a wirebond BGA package. However theelectrical performance of a wirebond BGA package at high speed (>5Gigabits per second (Gbps)) is relatively poor, such as having a poorinsertion loss and poor return loss.

Integrated circuit (IC) packages can be based on an emerging technologycalled a molded interconnect substrate (MIS). A MIS starts with aspecialized substrate material for select IC packages. The MIS itself isdeveloped and sold by various vendors, and a packaging house thengenerally takes the MIS and assembles an IC package around it includingadding molding. Some refer to the MIS as a leadframe.

MIS is different than traditional substrates, as MIS technologycomprises a pre-molded structure with one or more metal layers. Eachlayer is pre-configured generally with at least a top and a bottomcopper plating layer with a dielectric layer between copper layershaving vias to provide an electrical connections in the package.

SUMMARY

This Summary is provided to introduce a brief selection of disclosedconcepts in a simplified form that are further described below in theDetailed Description including the drawings provided. This Summary isnot intended to limit the claimed subject matter's scope.

Disclosed aspects solve the problem of the high cost of FC BGA packagesfor high speed devices because of the need to meet high electricalperformance (e.g., a 56 Gbps or more data rate) by developing a physicalstructure plus in-package DC blocking capacitors to provide a lessexpensive MIS QFN technology that has the MIS tuned to deliver similarperformance to a conventional FC BGA package. The disclosed performancetuning comprises narrowing the respective traces on the signal layer(e.g., negative (N) signal traces and positive (P) signal traces foreach channel) and providing a bottom metal layer with ground cuts, wherethe narrowed signal traces extend over the ground cuts and the DCblocking capacitors each have one plate over a ground cut.

Disclosed aspects include a packaged semiconductor device includes amolded interconnect substrate having a signal layer including a firstchannel and a second channel on a dielectric layer with vias, and abottom metal layer for providing a ground return path. The signal layerincludes contact pads, traces of the first and second channel includenarrowed trace regions, and the bottom metal layer includes a patternedlayer including ground cut regions. DC blocking capacitors are in serieswithin the traces of the first and second channel for providing ACcoupling, where the DC blocking capacitors have one plate over one ofthe ground cuts. An IC includes a first and a second differential inputchannel coupled to receive an output from the DC blocking capacitors,with a bump array thereon flip chip mounted to the contact pads toprovide first and second differential output signals.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, wherein:

FIG. 1A is a portion of an example packaged MIS QFN-based semiconductordevice without its molding that has two channels, and two traces perchannel for a total of four traces, each trace with a DC blockingcapacitor in series.

FIG. 1B is a schematic of a portion of a packaged MIS QFN-basedsemiconductor device shown in FIG. 1A.

FIG. 2 is a cross sectional view of an example packaged MIS QFN-basedsemiconductor device with its mold compound showing a signal path in thesignal layer for one of the differential inputs of a channel through aDC blocking capacitor shown as C1, according to an example aspect.

FIG. 3 is a close-up depiction of a portion of example packaged MISQFN-based semiconductor device without its molding with one DC blockingcapacitor removed to show a disclosed ground cut and disclosed ‘skinny’trace tuning.

FIGS. 4A-B compare simulated insertion loss between a known FC BGA-basedsemiconductor device in FIG. 4A and the insertion loss in FIG. 4B for anoriginal MIS QFN-based semiconductor device that lacks disclosedperformance tuning, and a MIS QFN-based semiconductor device thatincludes disclosed performance tuning. The specification to meet was<0.5 dB insertion loss at 14 GHz; <15 dB insertion loss at 14 GHz(pushing to <20 dB), with the device operating at 14 GHz (56 Gbps).

FIGS. 4C-D compare simulated return loss between a known FC BGA basedsemiconductor device in FIG. 4C and the insertion loss in FIG. 4D for anoriginal MIS QFN-based semiconductor device that lacks disclosedperformance tuning, and a MIS QFN-based semiconductor device thatincludes disclosed performance tuning.

DETAILED DESCRIPTION

Example embodiments are described with reference to the drawings,wherein like reference numerals are used to designate similar orequivalent elements. Illustrated ordering of acts or events should notbe considered as limiting, as some acts or events may occur in differentorder and/or concurrently with other acts or events. Furthermore, someillustrated acts or events may not be required to implement amethodology in accordance with this Disclosure.

FIG. 1A depicts a quarter (25%) of an example packaged MIS QFN-basedsemiconductor device 100 shown as a 2-channel device with a firstchannel and a second channel, comprising a MIS 220, with first, second,third and fourth direct current (DC) blocking capacitors C1, C2, C3 andC4, with two DC blocking capacitors per channel to provide a DC blockingcapacitor for blocking low frequency components for each of the inputs(one for P trace and one for N trace, or ‘legs’). An IC die 210 isattached to the MIS 220 by a bump array with a bump shown as 218. Thebump array can comprise copper pillars having solder bumps thereon thatare on bond pads of the IC die 210.

Although a mold compound is generally present for disclosed packagedevices, a mold compound is not shown in FIG. 1A to avoid obscuringfeatures. Also, although not shown, there are also input signals comingfrom the other end to the IC die 210, processed by the IC die 210, thenoutput from the first and second channel. As shown in the FIG. 1Bsimplified schematic, the IC die shown as IC die portion 210′ hasreceivers (Rx) 211 ₀, 211 ₁ and transmitters (Tx) 213 ₀, 213 ₁ coupledtogether by a clock data recovery (CDR) circuit 212 ₀, 212 ₁ that is forreconditioning the input signal and then outputting the reconditionedsignal.

The packaged semiconductor device 100 can generally comprise any devicethat is AC coupled with high speed signal paths that travel through theMIS 220 to and from the IC die 210. For example, a high speed signalconditioner, such as signal re-timer, or a signal repeater used in highperformance computing farm applications. Disclosed MIS QFN-basedsemiconductor devices can be tuned for use generally in anyserializer/deserializer (Serdes) or high speed channels.

The MIS 220 includes a signal layer 221 proving a top surface includingcontact pads that is on a dielectric layer 222 which has through-vias,and a bottom metal layer 223 that provides a ground return path, whichcan also be used for additional signal traces. Traces on the signallayer 221 routed though vias in the dielectric layer 222 to the bottommetal layer will be the physical bottom of the packaged MIS QFN-basedsemiconductor device which the customer generally solders (a patternedsolder layer is not shown in FIG. 1A, but see the patterned solder layer219 in FIG. 2 described below) to their printed circuit board (PCB)shown as PCB 240. The patterned solder layer can comprise solder ballsthat are attached to the bottom metal layer 223 of the MIS package 220or can comprise solder paste screen printed onto the PCB 240. Althoughnot shown, the MIS substrate 220 can include more than the 3 layersshown.

The signal layer 221 and a bottom metal layer 223 generally comprisecopper or a copper alloy. The dielectric layer 222 generally comprises amold compound as the dielectric material in-between layers 221 and 223.Molding compounds as known in packaging are generally compositematerials comprising epoxy resins, phenolic hardeners, silicas,catalysts, pigments, and mold release agents.

The MIS 220 provides a coplanar-waveguide (CPW) microstrip structure.The MIS 220 may be about 80 μm thick, with the signal layer 221 and thebottom metal layer 223 being about 20 μm thick, and the dielectric layer222 being about 40 μm thick. The DC blocking capacitors generally have acapacitance of 0.05 μF to 2 μF. This capacitance range is above thatgenerally possible for a capacitor on an IC, so that the DC blockingcapacitors are generally devices separate from the IC. A typicalcapacitance for the DC blocking capacitors is 0.22 μF in the 0201 size(0.6×0.3 mm).

FIG. 1B a simplified equivalent circuit for the differential inputchannels shown in FIG. 1A. For each of the channels there isdifferential signaling shown as an N trace and a P trace per channel,shown as RX0P and RX0N for the first channel, and RX1P and RX1N for thesecond channel. The bottom metal layer 223 provides a return path foreach of the signal traces to provide impedance matching. The signalitself is differential signaling, i.e., N and P. The gap/width of thetraces in the signal layer 221 are specifically chosen to maximize thedifferential transmission of signals.

At the input to the IC shown as IC die portion 210′ are the DC blockingcapacitors C1, C2, C3 and C4. The traces on the signal layer 221, viasin the dielectric layer 222, bumps (see FIG. 2 described below) andinterconnects in the path to connect to the IC die portion 210′ oneither side of C1, C2, C3 and C4 are represented by the solid linesshown. On the output side of the IC die portion 210′ there are 2 DCblocking capacitors per channel shown as C5, C6, C7 and C8, and thepackage traces on the signal layer 221, vias in the dielectric layer 222and bumps (see FIG. 2 described below) and interconnects in the path outfrom the IC die to the DC blocking caps are also represented by thesolid lines shown.

FIG. 2 is a cross sectional view of an example packaged MIS QFN-basedsemiconductor device 200 with its mold compound 260 showing a signalpath shown as ‘signal in’ with an arrow for one of the differentialinputs for a channel through the DC blocking capacitor shown as C1. TheIC die 210 has a bump array with one of the bumps 218 identified that isFC attached to contact pads on the signal layer 221 of the MIS. Outsidethe MIS QFN-based semiconductor device 200 there is a patterned solderlayer 219 such as solder balls on the bottom metal layer 223 which isexposed from the mold compound 260 on the bottom of the MIS 220 forcoupling the bottom metal layer 223 to lands on the PCB 240.

The arrows shown identifies the signal flow from the PCB 240 which is tothe patterned solder layer 219, to the bottom metal layer 223, to thevias in the dielectric layer 222, to a node on the signal layer 221, toone plate of C1. After passing through C1, the signal reaches the otherplate of C1 then another node on signal layer 221, to the bump 218(e.g., Cu pillar bump with solder), and finally into the IC die 210.

FIG. 3 is a close-up depiction of a portion of example packaged MISQFN-based semiconductor device 300 without its molding with DC blockingcapacitor C1 removed to show a disclosed ground cut 223 a and adisclosed skinny trace 221 s including over the ground cut 223 a, boththe ground cuts and skinny traces used for MIS performance tuning. Theground cut regions including the ground cut 223 a shown lack thedielectric layer 222 so that the capacitor plate over ground cut 223 ahas no bottom metal layer underneath. It is noted empty regions in FIG.3 are filled with dielectric, being mold compound (e.g., see moldcompound 260 in FIG. 2 described above).

For example, a nominal line width of 50 μm shown may be used for thesignal layer 221, while the skinny trace 221 s may have a width of 30 μmas shown, where this particular example arrangement represents theskinny trace 221 s having a 40% trace width reduction. A given deviceperformance requirement is met by tuning using the narrowing of traceson the signal layer 221 to provide skinny trace regions and ground cuts223 a, both generally used to meet a device specification, such asinsertion loss and return loss at a given operating frequency. For onespecific example specification, the specification is <0.5 dB insertionloss at 14 GHz; <15 dB at 14 GHz (pushing to <20 dB), with the deviceoperating at 14 GHz (56 Gbps).

The % range for trace narrowing on the signal layer 221 is 5% to 50%,such as a 25 μm skinny trace 221 s in standard 50 μm trace width. Asshown in FIG. 3, the width of the traces in the first signal layer 221may be 50 μm in general. However, when the first signal layer 221 tracecomes relatively close to the capacitor pads with one pad over a groundcut region, the trace width is significantly reduced, such as to 30 μmfor skinny trace tuning.

One plate of the DC blocking capacitors shown as C2 and C3 can be seento be over a ground cut 223 a. The metal pad on the signal layer 221 inthe box shown in FIG. 3 is used for attaching one of the plates of C1 ontop, just as C2 and C3 are attached to respective metal pads includingone of its plate over a ground cut 223 a.

Regarding tuning of the signal layer traces, the traces can befine-tuned according to the mold compound material properties. The widthof traces for the skinny traces of the signal layer 221 can be initiallypre-defined by theory and/or experience, and can then be pre-simulatedby a 2D field simulator to within several trace dimension candidates,which can then be validated by a full-wave 3D simulation on its endperformance. During all of these steps, the mold compound properties inthe dielectric layer 222 (its dielectric constant and loss tangent) areinput as parameters and the desired characteristic impedance Zo, whichis generally 50 ohm for single-ended and 100 ohm differentially.

Regarding the applicable theory, an empirical equation for the Zo of amicrostrip line copied below shows how the dielectric constant being onemold compound property as it is the dielectric in dielectric layer 222impacts the characteristic impedance of the signal layer 221 traces,which is recognized to be important for impedance matching, and thusdevice performance. The equation for a microstrip line shows therelationship between its characteristic impedance Zo, the dimensions ofthe traces, where W is the trace width, and d is the via thickness whichis set by the thickness of the dielectric layer 222 which fixes thedistance between the signal layer 221 and the bottom metal layer 223,and the dielectric constant €e of the dielectric layer 222.

$\begin{matrix}{Z_{0} = {\frac{60}{\sqrt{\in_{e}}}{\ln\left( {\frac{8d}{W} + \frac{W}{4d}} \right)}}} & {{{for}\mspace{14mu}\frac{W}{d}} \leq 1} \\{\frac{120\pi}{\sqrt{\in_{e}}\left\lbrack {\frac{W}{d} + 1.393 + {0.667{\ln\left( {\frac{W}{d} + 1.444} \right)}}} \right\rbrack}} & {{{for}\mspace{14mu}\frac{W}{d}} \geq 1}\end{matrix}$

Zo range is generally controlled to be 50 ohm single ended and 100 ohmdifferential as described above. The microstrip line as known in the artof radio frequency (RF) electronics usually has most of its field linesin the dielectric region, here the dielectric layer 222 concentratedbetween the signal layer 221 and the bottom metal layer 223. Theplacement of disclosed ground cuts is right beneath one of the capacitorpads so that every DC blocking capacitor has a pad with a ground cut.The same ground cut in the bottom metal layer 223 is also implementedbeneath the skinny traces. The DC blocking capacitor pads are generallyvery capacitive due to their coupling to the ground plane, so the groundcuts reduce the overall capacitive behavior of the package. There areground cuts also beneath the skinny traces on the signal layer 221 tofurther increase the inductance of the skinny traces.

FIGS. 4A-B compare the simulated insertion loss between a known FCBGA-based semiconductor device in FIG. 4A and the insertion loss in FIG.4B for an original MIS QFN-based semiconductor device that lacksdisclosed performance tuning, and a MIS QFN-based semiconductor devicethat includes disclosed performance tuning. The IC was a data centerre-timer used to extend the reach and robustness of long, lossy,crosstalk-impaired high-speed serial links while achieving a bit errorrate (BER) of 10 to 15 or less. The device specification was to meet was<0.5 dB insertion loss at 14 GHz; <15 dB at 14 GHz (pushing to <20 dB),with the device operating at 14 GHz (56 Gbps).

FIGS. 4C-D compare simulated return loss between a known FC BGA-basedsemiconductor device in FIG. 4C and in FIG. 4D the insertion loss for anoriginal MIS QFN-based semiconductor device that lacks disclosedperformance tuning and a MIS QFN-based semiconductor device thatincludes disclosed performance tuning.

The data in FIGS. 4A-4D demonstrates the problem of the high cost ofconventional FC BGA package technology used for high speed devicesbecause of the need to meet high electrical performance (56 Gbps+datarate) is solved as described herein by developing a physical MISstructure plus in-package DC blocking capacitors using a significantlyless expensive MIS QFN technology that can be tuned to deliver similarperformance to conventional FC-BGA based packaged devices. Disclosed MISQFN-based packaged devices provide the performance of conventionalFC-BGA package technology with about a 40 to 60% package cost reduction,and a production cycle time reduction of 1 to 2 weeks due to a speedierMIS process flow vs. conventional package substrate manufacturing.

Disclosed embodiments can be integrated into a variety of assembly flowsto form a variety of different packaged devices and related products.The assembly can comprise single semiconductor die or multiplesemiconductor die, such as PoP configurations comprising a plurality ofstacked semiconductor die. A variety of package substrates may be used.The semiconductor die may include various elements therein and/or layersthereon, including barrier layers, dielectric layers, device structures,active elements and passive elements including source regions, drainregions, bit lines, bases, emitters, collectors, conductive lines,conductive vias, etc. Moreover, the semiconductor die can be formed froma variety of processes including bipolar, insulated-gate bipolartransistor (IGBT), CMOS, BiCMOS and MEMS.

Those skilled in the art to which this Disclosure relates willappreciate that many other embodiments and variations of embodiments arepossible within the scope of the claimed invention, and furtheradditions, deletions, substitutions and modifications may be made to thedescribed embodiments without departing from the scope of thisDisclosure.

The invention claimed is:
 1. A packaged semiconductor device,comprising: a multi-layer molded interconnect substrate (MIS) having asignal layer including first and second traces for a first channel andfirst and second traces for a second channel on a dielectric layer withvias, and a bottom metal layer under the dielectric layer for providinga ground return path, the signal layer including contact pads, whereinthe first and second traces of the first and second channel includenarrowed trace regions and the bottom metal layer comprises a patternedlayer including a plurality of ground cut regions; a first and a seconddirect current (DC) blocking capacitor in series within the first andsecond traces of the first channel for providing alternating current(AC) coupling, the first and second DC blocking capacitors each with oneplate over one of the ground cuts; a third and a fourth DC blockingcapacitor in series within the first and second traces of the secondchannel for providing AC coupling, the third and fourth DC blockingcapacitors each with one plate over one of the ground cuts, and anintegrated circuit (IC) including a first differential input channelcoupled to receive an output from the first and second DC blockingcapacitors and at least a second differential input channel coupled toreceive an output of the third and fourth DC blocking capacitors, with abump array thereon flip chip mounted to the contact pads to providefirst and second differential output signals.
 2. The packagedsemiconductor device of claim 1, wherein the narrowed trace regions arenarrowed at least 20% as compared to a width of other traces on thesignal layer.
 3. The packaged semiconductor device of claim 1, whereinthe narrowed trace regions are narrowed at least 40% as compared to awidth of other traces on the signal layer.
 4. The packaged semiconductordevice of claim 1, wherein the bump array comprises copper pillarshaving solder bumps thereon.
 5. The packaged semiconductor device ofclaim 1, further comprising a printed circuit board (PCB) and a solderpattern between the bottom metal layer and the PCB, and a mold compoundproviding encapsulating for the packaged semiconductor device.
 6. Thepackaged semiconductor device of claim 1, wherein the IC comprises acommunication device comprising a receiver including a decoder and atransmitter including an encoder.
 7. The packaged semiconductor deviceof claim 1, wherein a capacitance of the first, second, third and fourthDC blocking capacitors is 0.05 μF to 2 μF.
 8. The packaged semiconductordevice of claim 1, wherein the narrowed trace regions are located over afirst of the ground cuts approaching the plate of the DC blockingcapacitors that is over the first ground cut.
 9. The packagedsemiconductor device of claim 1, wherein the dielectric layer comprisesa composite materials comprising an epoxy resin.
 10. A method offabricating a packaged semiconductor device, comprising: providing amulti-layer molded interconnect substrate (MIS) having a signal layerincluding first and second traces for a first channel and first andsecond traces for a second channel on a dielectric layer with vias, anda bottom metal layer under the dielectric layer for providing a groundreturn path, the signal layer including contact pads, wherein the firstand second traces of the first and second channel include narrowed traceregions and the bottom metal layer comprises a patterned layer includinga plurality of ground cut regions; attaching a first and a second directcurrent (DC) blocking capacitor in series within the first and secondtraces of the first channel for providing alternating current (AC)coupling, the first and second DC blocking capacitors each with oneplate over one of the ground cuts and a third and a fourth DC blockingcapacitor in series within the first and second traces of the secondchannel for providing AC coupling, the third and fourth DC blockingcapacitors each with one plate over one of the ground cuts, andattaching an integrated circuit (IC) including a first differentialinput channel coupled to receive an output from the first and second DCblocking capacitors and at least a second differential input channelcoupled to receive an output of the third and fourth DC blockingcapacitors, with a bump array thereon flip chip mounted to the contactpads to provide first and second differential output signals.
 11. Themethod of claim 10, wherein the narrowed trace regions are narrowed atleast 20% as compared to a width of other traces on the signal layer.12. The method of claim 10, wherein the narrowed trace regions arenarrowed at least 40% as compared to a width of other traces on thesignal layer.
 13. The method of claim 10, further comprising: designingthe narrowed trace regions according to dielectric properties of thedielectric layer; initially pre-defining a trace width for the narrowedtrace regions; pre-simulating using by a 2-dimensional field simulatorto within several trace width candidates, validating using a full-wave3-dimensional simulator for determining performance, wherein thedielectric properties of the dielectric layer and a thickness of thedielectric layer are input as parameters along with the trace width, anda desired characteristic impedance.
 14. The method of claim 10, whereinthe bump array comprises copper pillars having solder bumps thereon. 15.The method of claim 10, further comprising providing a printed circuitboard (PCB) and a solder pattern between the bottom metal layer and thePCB, and molding mold compound for providing encapsulating for thepackaged semiconductor device.
 16. The method of claim 10, wherein theIC comprises a communication device comprising a receiver including adecoder and a transmitter including an encoder.
 17. The method of claim10, wherein a capacitance of the first, second, third and fourth DCblocking capacitors is 0.05 μF to 2 μF.
 18. The method of claim 10,further comprising locating the narrowed trace regions over a first ofthe ground cuts approaching the plate of the DC blocking capacitors thatis over the first ground cut.